This invention relates to golf balls and a method for making golf balls having highly accurate and consistent dimensions and properties.
The production of golf balls involves several different steps, depending on the type of ball, such as three, two or one piece. According to the traditional method, a solid or composite elastomeric core is made, and an outer dimpled cover is formed around the core.
One method of applying a golf ball cover is by injection molding. The core is positioned centrally in a two part mold cavity and is held in a central position by retractable pins. The cover composition such as an ionomer is heated to a liquid and forced into the mold cavity through sprues located around the parting line between the mold halves. The surfaces of the mold halves have a number of protrusions or convex dimples arranged in a pattern, which cause corresponding dimples to be formed in the outer surface of the cover.
Upon cooling and removal from the mold, the golf ball comprises a central core surrounded by a dimpled cover of uniform thickness. In addition, however, the ball at this stage will include a number of solidified runners or flashing of cover material that extend from the sprues and the parting line seam of the mold halves. These solidified runners must be removed from the mold apparatus and must also be removed from the ball by a separate grinding or sanding operation. The sanding operation is imprecise and often causes irregularities on the ball surfaces.
After the flashings have been removed, the ball is painted with a known paint composition to attain a bright finish.
In view of the problems with flashing extending from the ball after the injection operation, it has been impossible to form dimples which extend across, or closely adjacent to the parting line. As a result, this may limit the number of dimple patterns which are available for the molding operation. One proposed solution to this problem is found in U.S. Pat. No. 4,653,758, in which two cover halves having undulating surfaces are fitted together within the mold. While this allows an improvement in the symmetry of the dimples, the ball will still have flashings, and no dimples may be placed on the juncture between the two cover halves.
Another problem arises in conjunction with the injection or other molding of golf ball exteriors, particularly when a number of opposed cavities are employed in a single machine. Heretofore, the mold cavities have been made by imprecise methods. Also, since the mold is repeatedly heated and cooled, some portions of the apparatus may expand and contract more than others. As a result, very often the mold halves of all molds cannot be brought into precise alignment prior to and during the injection operation. This, in return, results in defects, such as imperfect joinder at the parting line, or a ball which is out of round, or an outer surface which is not concentric with the spherical inner core.
All of the foregoing problems in commercial golf ball production result in balls having inconsistent performance. With the advent of more advanced golf equipment to allow better consistency and accuracy, it would be desirable to have parallel advances in the art of making golf balls.